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Windows Server 2012 R2 brought us the ability to resize virtual disks on line. This was a long sought after feature for many of us. It can be done via the GUI or with PowerShell. I do note however that quite often people have some problems when first using this capability. So we’ll go over the rules & prerequisites here.

Listed below are the important factors to keep in mind

It has to be a VHDX

Works for both generation 1 and generation 2 virtual machines

It needs to be attached to a vSCSI controller. Remember this when dealing with with generation 1 virtual machines. In particular note that this means you cannot live resize the system disk as that IDE only (can’t boot from SCSI in generation 1).

The virtual disk cannot be a shared VDHX (it’s on my feature request list for vNext)

You can extend a virtual disk

You can shrink a virtual disk

This feature can leverage ODX for speed when available. The speed of this is quite addictive.

Some notes where people seem to make some other mistakes

You’ll note that you cannot shrink a virtual disk that has no unallocated disk space on the disk inside the virtual machine. When you see this picture inside of the virtual machines you can shrink your VHDX if all the above factors are in order.

If there is no unallocated disk space the option to shrink the VHDX won’t even show up in the GUI.

This means you’ll first need to shrink the volume inside the virtual machine if all disk space has already been allocated.

(Like wise don’t forget to expand the volume inside the VM to be able to use the added space you see show up as unallocated space on the disk.)

The below image is a great summary of the above

Legacy OS in the VM?

It’s also important to note that an OS inside a VM (Windows Server 2003 comes to mind) that does not allow the expansion or shrinking of volumes means you will need a 3rd party tool to do the same. I use GParted, a free partition editor for these scenarios.

A Last ditch Effort

Fist of all you need to realize this might not work. It’s a last ditch effort. There is a reason why you have backups (with tested restores) and why you should monitor your environment for things that are not as they should be. Early intervention can pay off.

Also see blog post on a couple of more preferred actions.

If you have lost checkpoints, you have basically lost data and corruption/data inconsistencies are very much a possibility and reality. If the files have been copied and information about what file is the parent the dates/timestamps are what you have to go by. You might not know for sure if you have them all.

Setting up the demo

For demo purposes we take a test VM and ad files to indicate what checkpoint we’re at.

We start with ORGINAL.TXT on the desktop and we create a checkpoint, which we rename accordingly.

We add a file called CHECK01.TXT and we create a checkpoint, which we rename accordingly.

We add a file called CHECK02.TXT and we create a checkpoint, which we rename accordingly.

We add a file called NOW.TXT no more checkpoints are taken.

The file names represent the content you’d see disappear if you applied the checkpoint and we have reflected this in the name for the checkpoints.

As we want to merge all the snapshots and and up with a usable VHDX we’ll work back from the most recent differencing disk until all is merged. As you can see this is a straight forward situation and I hope you’ll never be running having to deal with a vast collection of sub trees .

Finding out what are the parents of avhdx files

In this demo it’s pretty obvious what snapshot exist and what avhdx files they represent. We’ve even shown you the single tree visualized in Hyper-V Manager. In reality bad things have happened and you don’t see this information anymore. So you might have to find out yourself. This is done via inspect disk in Hyper-V manager. I you’re confused about what the parent is of (a)vhdx files this tool will help you find out or show you what the most recent one was.

Sometimes the original files have been renamed or moved and that it will show you’re the last known valid parent.

Manually Merging the checkpoints

Remember to make a copy of all files as a backup! Also make sure you have enough free diskspace … you need working space! You might need another shot at this. As we want to merge all the snapshots and and up with a usable VHDX we’ll work back from the most recent differencing disk until all is merged in the oldest one which is the vhdx. You can look at the last modified time stamps to find out the correct order in which to work. The most recent avdx is the one used in the virtual machine configuration file and locate the information for the virtual hard disk.

The configuration file’s avhdx is the one containing the “NOW” running state of the VM.

Note: You might find some information that you need to rename the extension avhdx to vhdx (or avhd to vhd). The reason for this was that in Windows 2008 Hyper-V Manager did not show avhd files in the Edit virtual disk wizard. You can still do this and it will still works, but you do not need to. Ever since Windows Server 2008 R2 avhd (and with since Windows Server 2012 avhdx) files do show up in Hyper-V Managers Disk edit.

WARNING: If you did not start with the most recent one and work your way down, which is the easiest and least confusing way all is not lost. But you will have to reconnect the first more recent (a)vhdx to one to it’s new parent. This is needed as by merging a snapshot out of order more recent one will have lost it’s will have lost it’s original parent.

Here’s how to do this: Select reconnect. This is the page you’ll get if you’d start edit disk wizard as all other option are unavailable due to the missing parent.

The wizard will tell you what used to be the parent and allow you to select a new one. Make sure to tick the check box for Ignore ID mismatch or the reconnect will fail as you’re previous out of order merge has created a new a(vhdx). If your in this pickle by renaming (a)vhdx files or after a copy this isn’t needed by the way.

Follow the wizard after that and when your done you can launch the edit disk wizard again and perform a merge. It’s paramount that you do not mix up orders when doing so that you reconnect to the parent this or you’ll end up in a right mess. There are many permutations, keep it simple!. Do it in order . If you start having multiple checkpoint trees/subtrees things can get confusing very fast.

You might also have to reconnect if the checkpoints have lost their connection the what they know to be their last parent for other reasons. In that case you do this and when that’s done, you merge. Rinse and repeat. The below walk through assumes you have no reconnects to be done. If so it will tell you like in the example above.

Walk trough:

Open the Edit Disk Wizard

Select the most recent avhdx & click “Next”

We choose to merge the avhdx

In our case into its parent disk

Verify the options are correct and click “Finish”

Let the wizard complete

That’s it. You’ve merged the most recent snapshot into it’s parent. That means that you have not lost the most recent state of the virtual machine as when it was running before you shut it down. This can be verified by mounting the now most recent avhdx and looking at the desktop for my user profile. You can see the NOW.txt text file is there!

OK, dismount the avhdx and now it’s rinse and repeat.

You do this over an over again until your merge the last avhdx into the vhdx.

Than you have the vhdx you will use to create a new virtual machine.

Make sure you get the generation right.

Assign memory

Connect to the appropriate virtual switch or not if you’re not ready to do this yet

Use your vhdx disk that’s the remaining result of your merging efforts

When you boot that virtual machine you’ll see that all the text files are there. It’s as if you’ve deleted the checkpoints in the GUI and retained “NOW” in the vhdx.

Last but not least, you can use PowerShell or even DiskPart for this but I found that most people in this pickle value a GUI. Use what you feel most comfortable with.

Thanks for reading and hope this helps someone. Do remember “big boy” rules apply. This is not safe, easy or obvious in each and every situation so you are responsible for everything you do in your environment. If your in to deep, way over your head, etc. call in some expert help.

Lingering or phantom Hyper-V checkpoints or snapshots

Once in a while the merging of checkpoints, previously known as snapshots, in Hyper-V goes south. An example of this is when checkpoints are not cleaned up and the most recent avhdx or multiple of these remains in use as active virtual disk/still even as you don’t see them anymore as existing in the Hyper-V Manager UI for example. When that happens you can try looking at the situation via PowerShell to see if that show the same situation. Whatever the cause, once in while I come across virtual machines that have one or more avhdx (or avdh) active that aren’t supposed to be there anymore. In that case you have to do some manual housekeeping.

Now please, do not that in Windows Server 2012(R2) Hyper-V replica is using checkpoints and since Windows Server 2012 R2 backups also rely on this. Just because you see a snapshot you didn’t create intentionally, don’t automatically think they’re all phantoms. They might exits temporarily for good reason . We’re talking about dealing with real lingering checkpoints.

Housekeeping

Housekeeping comes in a couple of variants form simply dusting of to industrial cleaning. Beware of the fact that the latter should never be a considered a routine operation. It’s not a normal situation. It’s a last ditch resort and perhaps you want to call support to make sure that you didn’t miss anything else.

Basically you have tree options. In order of the easiest & safest to do first these are:

Create a new checkpoint and delete it. Often that process will take care of merging the other (older) lingering avhd/avhdx files as well. This is the easiest way to deal with it and it’s as safe as it gets. Hyper-V cleans up for you, you just had to give it a kick start so to speak.

Shut down the VM and create a new checkpoint. Export that newly created checkpoint. Yes you can do that. This will create a nicely exported virtual machine that only has the relevant vhd/vhdx files and no more checkpoints (avhd/avhdx). Do note that this vhd/vhdx is dynamically expanding one. If that is not to your liking you’ll need to convert it to fixed. But other than that you can dump the old VM (don’t delete everything yet) and replace it by importing the one you just exported. For added security you could first copy the files for save guarding before you attempt this.

Do manual mergers. This is a more risky process & prone to mistakes. So please do this only on a copy of the files. That way you’ll give Microsoft Support Services a fighting change if things don’t work out or you make a mistake. Also note that in this case you get one or more final VHDX files which you’ll use to create a new virtual machine with to boot from. It’s very hands on.

So that’s the preferred order of things to try/do in regards to safety. The 3rd option, is the last resort. Don’t do it before you’ve tried options 1 and 2. And as said above, if you do need to go for option 3, do it on copies.If you’re unsure on how to proceed with any of this, get an expert involved.

There’s actually another option which is very save but not native to Hyper-V. In the running virtual machine which current state you want to preserve do a V2V using Disk2vhd v2.01. Easy and sort of idiot proof if such a thing exists.

In a next blog post I’ll walk you through the procedure for the 3rd option. So if this is your last resort you can have practiced it before you have to use it in anger. Bit please, if needed, and do make sure it’s really needed as discussed above, try 1 first. If that doesn’t do it. Then try option 2. If that also fails try option 3. Do not that for option 2 and 3 you will have to create a new virtual machine with the resulting VHDX, having the required settings documented will help in this case.

This question came up recently, once again, and deserves it a little blog post. If you want to see the benefits of ODX you’ll need to connect your virtual disks to a vSCSI controller or other supported controller option. These are iSCSI, vFC, a SMB 3 File Share or a pass-through disk. But unless you have really good reason to use pass-through disks, don’t. It’s limiting you in to many ways.

Basically in generation 1 virtual machines that boot from a vIDE this rules out the system disk. So the tip here is to store your data that’s moved around in or between virtual machines in vSCSI attached VDH or (preferably) VHDX virtual disks. If you can use generation 2 virtual machines, you’ll be able to leveraged ODX on the system partition as well as it boots from vSCSI .

It goes without saying you need to store any virtual disks involved on ODX capable LUNs via iSCSI, FC, FCoE, SMB 3 File Share or SAS for ODX to be available to the virtual machine.

Also beware that ODX only works on NTFS partitioned disks. The files cannot be compressed or encrypted. Sparse files are not supported either. And finally, the volume cannot be BitLocker protected.

Here’s a screenshot of a copy of 30GB worth of ISO files to a VHDX attached to a vSCSI controller:

Here’s a screenshot of a copy of 30GB worth of ISO files to a VHDX attached to a vIDE controller.

You’ll notice quite a difference. Depending on the load on the controllers/SAN it’s on average 3 times slower than the same action to a VHDX disk on a vSCSI controller.